1. Field of the Invention
This invention relates to a pressure responsive valve mechanism for preventing undesired escape of fuel vapor from the fuel tank in an automotive vehicle during refueling.
2. Description of Prior Developments
During normal operation of automotive vehicles such as cars, trucks, buses and vans, the fuel tank often becomes slightly pressurized due to the accumulation of fuel vapor in the confined space above the liquid fuel. This pressurized condition is especially likely during hot weather periods when the fuel vapor pressure is higher. When liquid fuel is added to the fuel tank, the pressurized vapor has an open path to the atmosphere via the opened closure cap at the mouth of the fuel tank filler tube. The pressurized vapor can flow rapidly out through the tube, thereby polluting the ambient atmosphere. Such escape of the vapor can be detected as an audible hissing sound associated with rapid outflow of fuel vapors through the filler tube.
A venting mechanism shown in U.S. Pat. No. 4,572,394 issued to T. Tanahashi, et al addresses the problem of fuel vapor escape during refueling by providing a canister of activated charcoal around the mouth of the filler tube. In contrast, the newly proposed mechanism described in detail below is adapted to use a conventional activated charcoal canister used for venting the fuel tank during normal vehicle operation. Moreover, the newly proposed arrangement locates a control valve remote from the fuel tank and filler tube where possible clog-up due to atmospheric contamination is not as likely as in the case of the patented arrangement of Tanahashi, et al.
Also, the newly-proposed arrangement includes a rigid rugged guide structure for a fuel dispenser nozzle, whereas the arrangement of the '394 patent includes a rubber bellows guide structure for the nozzle. Service life of the guide structure in U.S. Pat. No. 4,572,394 could be a problem.